The present invention relates to a driver bit and a screw for use therewith. More particularly, it relates to a combination of a driver bit and a screw fitting the driver bit which combination effects tight mating of crossed flutes or bit mate flutes formed on the screw head portion and the driver bit fitting the flutes and always enables quick positive screwing and unscrewing by transmission of appropriate torque.
Conventionally known are the combinations of typical screws and driver bits as shown in FIGS. 13 to 16. That is, FIGS. 13 and 14 show a conventional screw with crossed flutes; FIG. 15 shows a driver bit for use with the screw with crossed flutes; and FIG. 16 shows the aforementioned screw and driver bit, mated with each other.
A prior art screw 10 shown in FIG. 13 is provided, on a screw head portion 10a thereof, with crossed flutes 12. The crossed flutes 12 are provided with constantly inclined flute portions 12a, each extending from the end portion towards the central portion of a screw neck portion l0b. The crossed flutes 12 are also provided, on a bottom portion thereof, with a substantially conical bottom surface 14 inclined gradually. Incidentally, reference numeral 13 designates tapered sidewall portions formed between adjacent crossed flutes 12. That is, the tapered sidewall portions 13 engageably contact with the blade portions of a driver bit, which is described later. In addition, at the corners adjoining the respective inclined flute portions 12a, tapered coupling surfaces 17a, 17b are formed which extend from the position of the conical bottom surface 14 to the opening rim portions of the crossed flutes 12 on the screw head portion 10a. These tapered coupling surfaces 17a, 17b are also adapted to engageably contact part of the blade portions of the driver bit, which is described later.
On the other hand, a prior art driver bit 20 shown in FIG. 15 is provided with blade portions 22 to fit the crossed flutes 12 of the aforementioned screw 10. The driver bit 20 is also provided with extended blade portions 22a each extended so as to fit the shape of the inclined flute portions 12a that are formed to orient towards the central portion of the screw neck portion 10b from the end portions of the aforementioned crossed flutes 12. Incidentally, reference numeral 23 designates tapered sidewall portions that are formed on the both sides of the aforementioned respective blade portions 22 or extended blade portions 22a. That is, the tapered sidewall portions 23 engageably contact with the tapered sidewall portions 13 formed in the crossed flutes 12 of the aforementioned screw 10.
According to the combination of the prior art screw and driver bit formed as such, when the screw 10 and the driver bit 20 are fit to each other as shown in FIG. 16, the blade portions 22 of the driver bit 20 and extended blade portions 22a fit into the inclined flute portions 12a of the crossed flutes 12, respectively, as described above. The sidewall portions 23 of the aforementioned blade portions 22 and extended blade portions 22a are brought into contact with the tapered sidewall portions 13 of the crossed flutes 12 of the screw 10. Thus, rotating the driver bit 20 allows a predetermined torque to be transmitted to the screw 10. That is, screwing and unscrewing can be achieved on a desired target object to be screwed.
However, according to the combination of the prior art screw 10 and the driver bit 20 formed as described above, the crossed flutes 12 of the screw head portion 10a form constantly inclined flute portions 12a orienting towards the central portion of the screw neck portion 10b from the end portions thereof. On the other hand, for the driver bit 20 corresponding thereto, the ridge portions of the extended blade portions 22a fit the shape of the aforementioned inclined flute portions 12a to fit into the aforementioned crossed flutes 12. Moreover, the ridge portions of the extended blade portions 22a are made wider gradually backwards from the distal end portion thereof. Furthermore, the tapered sidewall portions 23 formed on the respective blade portions 22 of the driver bit 20 are also engageably brought into contact with the tapered sidewall portions 13 formed in the crossed flutes 12 of the screw 10. Accordingly, since the aforementioned driver bit 20 and the crossed flutes 12 can be said to be totally in taper contact with one another, rotating the aforementioned driver bit 20 in a predetermined direction causes the distal end of the driver bit 20 to fly outwardly along the inclined surface of the inclined flute portions 12a of the aforementioned crossed flutes 12 (shown by an arrow in FIG. 16), resulting in the so-called xe2x80x9ccome-out phenomenonxe2x80x9d.
In particular, as shown in FIG. 14, the shape of the crossed flutes of a prior art screw is formed in such a manner that the respective crossed flutes 12 are made relatively larger in width than the ridge portions of the extended blade portions 22a of the driver bit 20 in order to facilitate mating the distal end of the driver bit 20 with the crossed flutes. On the other hand, the area of the tapered sidewall portions 13 and the tapered coupling surfaces 17a, 17b, formed at a boundary portion or corner portions between adjacent crossed flutes 12, 12, is relatively small. Accordingly, rotating the aforementioned driver bit 20 causes a great amount of stress to be loaded on the aforementioned tapered sidewall portions 13 and the tapered coupling surfaces 17a, 17b. Thus, as shown in FIG. 14 with shaded portions 15, great fastening resistance would cause the aforementioned tapered sidewall portions 13 and the tapered coupling surfaces 17a, 17b to be gradually damaged. Therefore, an increase in the damaged portions (the shaded portions 15) would make the come-out phenomenon to occur frequently in the aforementioned driver bit 20, making it impossible to effect screwing.
From these points of view, it is necessary to apply thrust to the driver bit 20 to strongly press the bit against the flute portions 12a at the time of rotating the driver bit 20 in order to prevent the come-out phenomenon in the aforementioned driver bit 20. However, pressing the bit as such would cause screwed target objects, particularly such as precision parts, to be broken or damaged although no problem will occur if the target objects are rigid bodies such as meal.
In addition, the occurrence of the aforementioned come-out phenomenon would cause the distal end portion of the bit or the blade portions 22 and extended blade portions 22ato be worn quickly. The wear would cause the aforementioned come-out phenomenon to occur more frequently, resulting in an increase of the damage of the screw flutes.
Furthermore, applying an excessive thrust to the aforementioned driver bit 20 could be useful to prevent the aforementioned come-out phenomenon. However, this would make it impossible to transmit precise torque to the screw, and thus operators would apply different amount of thrust to the driver bit 20. Consequently, torque for fastening screws would become greatly different from operator to operator.
Still furthermore, when tapping screws are screwed into a target object made of synthetic resin or the like, friction caused by the thrust would be added to that by the rotation of the screw. This would cause a great amount of heat to be produced to such an extent as to reduce the hardness of the screwed portion of the target object, thereby causing the screw to become loose or the target object to be damaged.
On the other hand, when screwing is carried out manually, rotating the driver bit 20 while sufficiently pressing the driver bit 20 against the screw would require a great amount of effort of the operator and make the operator exhausted.
In addition, according to the combination of the aforementioned prior-art screw 10 and the driver bit 20, when screwing is carried out with a manual tool or an electric tool, it is difficult to rotate the screw while maintaining the screw axis and the driver bit axis in proper alignment with each other at the time of fitting the distal end potion of the bit to the screw flutes. Therefore, when the screw axis is inclined relative to the driver bit axis, not only the aforementioned come-out phenomenon but also damage to the screw flutes will occur frequently.
Furthermore, at the time of unscrewing, like in the foregoing, the come-out phenomenon and damage to the screw flutes will be likely to occur. However, in this case, it will become impossible to remove the screws, thus resulting in such a situation as to break part of the target object to be unscrewed. In particular, when dust particles clog the screw flutes, the aforementioned situation occurs more frequently.
From these points of view, the present applicant previously suggested the combination of screws and driver bits which can effectively prevent the come-out phenomenon of the driver bit and damage to screws as occurred conventionally (Japanese Patent Laid-Open Publication No.Hei 8-145024 and No.Hei 9-177743). In addition, the combination can always provide appropriate and quick screwing and thus make it possible to significantly improve the efficiency of screwing even when damage has occurred to the bit mate flutes of the screw. This is achieved by improving the structure of the flute portions of the bit mate flutes of the screw in the combination of the screw and the driver bit.
The combination of a screw and a driver bit according to Japanese Patent Laid-Open Publication No.Hei 8-145024 is formed as shown in FIG. 12(b). That is, vertical end wall portions 32a of a predetermined depth are formed at the end portions of the bit mate flutes 32 of the screw head portion 30a. Horizontal stepped portions 32b are provided from the vertical end wall portions. Inclined flute portions 32c are provided to orient towards the central portion of the screw neck portion 30b from these horizontal stepped portions 32b. Alternatively, tapered or curved flute portions are extendedly formed to orient towards the central portion of the screw neck portion 30b from the aforementioned vertical end wall portions. In addition, a substantially conical bottom surface 34 is formed at the bottom portion thereof. The screw is thus formed to fit the driver bit comprising wing portions for engaging the vicinity of the aforementioned stepped portions or the curved flute portions (refer to FIG. 12(a)).
That is, referring to FIG. 12(b), right-angle rim portions 42a and extended wing portions 42b formed at wing portions 42 of a driver bit 40 fit into the horizontal stepped portions 32b and the inclined flute portions 32c of the bit mate flutes 32 of the screw 30, respectively. Then, sidewall portions 43 of the aforementioned wing portions 42 and extended wing portions 42b are brought into contact with the sidewall portions 33 of the bit mate flutes 32 of the screw 30. Thus, rotating the driver bit 40 allows a predetermined torque to be transmitted to the screw 30.
The combination of a screw and a driver bit according to Japanese Patent Laid-Open Publication No.Hei 9-177743 is formed as shown in FIG. 12(c). That is, vertical end wall portions 32a of a predetermined depth are formed at the end portions of the bit mate flutes 32 of the screw head portion 30a. Non-planar bottom portions are formed which are raised towards the central portion of the screw head portion from the lower rim portions of these vertical end wall portions. Inclined flute portions 32c are formed towards the central portion of the screw neck portion from these raised portions of the non-planar bottom portions. In addition, a substantially conical bottom surface is formed at the bottom portion thereof. The screw is thus formed to fit the driver bit comprising blade portions formed like in the foregoing (refer to FIG. 12(a)).
That is, referring to FIG. 12(c), horizontal surface portions 42a and projections 42b formed at flat blade portions 42 of a driver bit 40 fit into the non-planar bottom portions 32b and the inclined flute portions 32c of the bit mate flutes 32 of the screw 30, respectively. Then, sidewall portions 43 of the aforementioned blade portions 42 and projections 42b are brought into contact with the sidewall portions 33 of the bit mate flutes 32 of the screw 30. Thus, rotating the driver bit 40 allows a predetermined torque to be transmitted to the screw 30.
For the driver bit 40 according to the aforementioned respective suggestions, the horizontal stepped portions 32b or non-planar bottom portions 32b are formed at the bit mate flutes 32 of the screw 30. Thereby the contact area of the sidewall portions 33 of the bit mate flutes 32 which is brought into contact with the wing portions 42 of the driver bit 40 or the sidewall portions 43 of the flat blade portions 42 can thereby be increased. On the other hand, the tapered contact area in which the inclined flute portions 32c of the bit mate flutes 32 of the screw 30 are brought into contact with the extended wing portions 42b or the projections 42b of the driver bit 40 is only partial and small. Accordingly, the come-out phenomenon that occurs in the combination of a prior art screw and a driver bit can be positively prevented.
However, even the combinations of the screws and the driver bits according to the aforementioned suggestions are not still satisfactorily sufficient to effect more smoothly and quickly the mating of the distal end portion of the driver bit with the bit mate flutes formed on the screw head portion.
That is, in the structure of the driver bit 40 previously suggested, it was found that the distal end portion of the aforementioned flat blade portions 42 slidingly chafes against the surface of the screw head portion to damage the surface when the flat blade portions 42 comprising the horizontal surface portions 42a, extending substantially at a right angle, engaged with the vertical end wall portions 32a formed at the end portions of the aforementioned bit mate flutes 32 fit into the bit mate flutes 32 formed on the head portion of the screw 30 while rotating the aforementioned driver bit.
Furthermore, even when the distal end of the aforementioned driver bit 40 fits into the bit mate flutes 32 of the screw head portion 30a, the come-out phenomenon is sometimes caused to occur. That is, in the combination of the driver bit shown in FIG. 12(a) and the screw shown in FIG. 12(b), for example, right-angle crossovers between the aforementioned vertical end wall portions 32a and the horizontal stepped portions 32b are sometimes raised due to the wear produced by a header punch for punching the bit mate flutes 32 when the horizontal stepped portions 32b extending at a right angle from the vertical end wall portions 32a of a predetermined depth formed at the end portions of the bit mate flutes 32 of the screw head portion 30a are not properly formed in mass production of the screw. In the case like this, it was found that the distal end of the aforementioned driver bit 40 could not sufficiently fit into the bit mate flutes 32 of the screw head portion 30a, resulting in an unstable fitting and potentially causing the come-out phenomenon to occur while rotating the driver bit 40.
On the other hand, in the combination of the driver bit shown in FIG. 12(a) and the screw shown in FIG. 12(c), the bit mate flutes 32 includes non-planar bottom portions 32b in place of the aforementioned horizontal stepped portions 32b to set to a deeper dimension. This makes it possible to avoid the aforementioned come-out phenomenon. However, since the strength of the screw neck portion 30b was reduced, it was found that the screw head portion 30a could be cut off at the time of fastening operation with driver bit 40.
Accordingly, the present inventor has made intensive studies and pilot productions. Consequently, in a driver bit fit for a screw with substantially vertical end wall portions of a predetermined depth, the wall portions being formed at end portions of bit mate flutes of a screw head portion, with substantially planar bottom portions formed to orient towards a central portion of a screw neck portion from lower rim portions of the vertical end wall portions, and with a conical bottom surface formed at the central portion, the present inventor formed the driver bit in such a manner that the aforementioned driver bit comprises flat blade portions having substantially vertical end portions for fitting a distal end portion thereof into the bit mate flutes of the screw head portion along the vertical end wall portions, and a distal end face of the flat blade portions is formed as a conical projected portion inclined at an angle of from 1 to 45xc2x0 relative to the horizontal or preferably at an angle of from 25 to 35xc2x0. By forming the driver bit as such, when the distal end of the aforementioned flat blade portions slidingly chafes against the surface of the screw head portion at the time of mating the driver bit with the bit mate flutes formed on the screw head portion while rotating the driver bit, it was found that the surface would not be damaged at all and the distal end of the flat blade portions fits into the screw, thereby preventing positively the come-out phenomenon even while the driver bit was being rotated.
On the other hand, as a screw that fits the aforementioned driver bit, used is a screw comprising end portions of bit mate flutes of a screw head portion, formed as vertical end wall portions with a predetermined depth; stepped portions formed at lower rim portions of the vertical end wall portions; inclined flute portions formed to incline towards a central portion of a screw neck portion; a conical bottom surface formed at the center thereof, wherein the aforementioned bit mate flutes become wider radially outwardly from the central portion of the screw head portion, and an opening angle between sidewall portions of the aforementioned adjacent respective flutes, facing to each other, is an acute angle slightly smaller than a right angle. When the blade portions of the driver bit are brought into contact with the respective sidewall portions of the bit mate flutes of the screw, formed to become wider outwardly, it was found that the clearance between the blade portions and the flutes could be made as small as possible to achieve appropriate mating of the screw with the driver bit and the come-out phenomenon could be reliably prevented.
Furthermore, as a screw that fits the aforementioned driver bit, used is a screw comprising stepped portions provided for end portions of bit mate flutes of a screw head portion; inclined flute portions extendedly formed to orient towards a central portion of a screw neck portion from these stepped portions; a substantially conical bottom surface formed at a bottom portion thereof; and wall portions formed at the end portions of the aforementioned bit mate flutes and recessed inwardly over a predetermined depth from the vertical and recessed substantially in the shape of xe2x80x9c less than xe2x80x9d in cross section. It was found with the screw that the portions recessed from the vertical always served as a gap portion and thus dust particles or foreign objects could be removed by pushing them into the aforementioned gap portion. It was also found that the degrees of freedom of the distal end of the driver bit were expanded at the time of mating the driver bit with the screw and the distal ends of the blade portions could be always appropriately mated with the screw, thereby making it possible to facilitate smooth screwing and unscrewing.
Therefore, an object of the present invention is to provide a combination of driver bits and screws which can prevent damage caused by slidingly chafing against the surface of a screw head portion and which can prevent positively a come-out phenomenon in fitting with a screw, thereby always effecting appropriate and quick screwing and thus providing significantly improved working efficiency.
In order to achieve the aforementioned objects, the driver bit according to the present invention is a driver bit fit for a screw with substantially vertical end wall portions of a predetermined depth, the wall portions being formed at end portions of bit mate flutes of a screw head portion, with substantially planar bottom portions formed to orient towards a central portion of a screw neck portion from lower rim portions of the vertical end wall portions, and with a conical bottom surface formed at the central portion thereof,
the aforementioned driver bit characterized by comprising flat blade portions having substantially vertical end portions for fitting a distal end portion thereof into the bit mate flutes of the screw head portion along the vertical end wall portions, wherein
a distal end face of the flat blade portions is formed as a conical projected portion inclined at an angle of from 1xc2x0 to 45xc2x0 relative to the horizontal.
In this case, the aforementioned conical projected portion at the distal end face of the flat blade portions can be formed to incline at an angle of from 25xc2x0 to 35xc2x0 relative to the horizontal.
Moreover, the aforementioned conical projected portion at the distal end face of the flat blade portions can be so formed as to make the conical surface thereof a single tapered surface or multi-stepped tapered surfaces.
Furthermore, the aforementioned conical projected portion at the distal end face of the flat blade portions can have the conical surface formed in the shape of a convex or a concave in cross section.
On the other hand, both sidewall portions at the distal end of the flat blade portions can be so formed as to become wider outwardly in order to fit the bit mate flutes of the screw formed to become wider radially outwardly from the central portion of the screw head portion.
In addition, at least one of the flat blade portions can be provided with a notch extending from the distal end face thereof in the direction of the bit axis and having a predetermined length.
On the other hand, a screw which fits the driver bit according to the present invention is characterized by comprising stepped portions provided for end portions of bit mate flutes of a screw head portion, inclined flute potions extendedly formed to orient towards a central portion of a screw neck portion from the stepped portions, a substantially conical bottom surface formed at a bottom portion thereof, and wall portions formed at the end portions of the aforementioned bit mate flutes and recessed inwardly over a predetermined depth from the vertical.
In this case, the wall portions formed at the end portions of the bit mate flutes can be recessed substantially in the shape of xe2x80x9c less than xe2x80x9d in cross section.
In addition, the bit mate flutes can be formed to become wider radially outwardly from the central portion of the screw head portion and an opening angle between sidewall portions of the aforementioned adjacent respective flutes, facing to each other, can be an acute angle slightly smaller than a right angle.
Furthermore, as a screw that fits the driver bit according to the present invention, such a plus/minus screw can be used in which a screw head portion is provided with crossed bit mate flutes; one of straight flutes of the crossed bit mate flutes is so formed as to allow blade portions of a plus driver bit to fit therein; the other straight flute is so formed as to allow blade portions of a minus driver bit to fit therein; substantially vertical end wall portions of a predetermined depth are formed at end portions of the aforementioned one of the straight flutes; and wall portions are formed substantially in the shape of xe2x80x9c less than xe2x80x9d in cross section on the aforementioned vertical end wall portions over a predetermined depth and recessed inwardly from the vertical.
In addition, the present invention is characterized by combining the driver bit formed as described above and a screw comprising end portions of bit mate flutes of a screw head portion, formed as vertical end wall portions with a predetermined depth; stepped portions formed at lower rim portions of the vertical end wall portions; inclined flute portions formed to incline towards a central portion of a screw neck portion; a conical bottom surface formed at the center thereof. The screw is formed such that the aforementioned bit mate flutes become wider radially outwardly from the central portion of the screw head portion; and an opening angle between sidewall portions of the aforementioned adjacent respective flutes, facing to each other, is an acute angle slightly smaller than a right angle.
Furthermore, the present invention is characterized by combining the driver bit and a screw comprising horizontal bottom portions or inclined flute portions formed to orient towards a central portion of a screw neck portion from lower rim portions of end portions of bit mate flutes on a screw head portion; a conical bottom surface formed at the central portion thereof; and wall portions formed at the end portions of the aforementioned bit mate flutes and recessed inwardly over a predetermined depth from the vertical.
Still furthermore, the present invention is characterized by combining the driver bit and a plus/minus screw in which a screw head portion is provided with bit mate flutes composed of crossed flutes; one of straight flutes of the crossed bit mate flutes is so formed as to allow blade portions of a plus driver bit to fit therein; the other straight flute is so formed as to allow blade portions of a minus driver bit to fit therein; and substantially vertical end wall portions of a predetermined depth are formed at end portions of the aforementioned one of the straight flutes.
In this case, the aforementioned plus/minus screw can be formed such that the one straight flute of the bit mate flutes is formed substantially to become wider outwardly; a flute is formed substantially to become wider outwardly in the other straight flute; and blade portions of a driver bit are brought into contact with respective side wall portions of the aforementioned flutes made wider outwardly, at the same time and with equal clearances.